Authorities have cut off the water supply of over 1 million people in a northern Chinese city due to an industrial leak. Residents were not notified of the spill for days, despite the public health threat it posed.

­Handan, located in Hebei province, has seen its primary water supply cut off since Saturday afternoon. The move followed an accident in nearby Shanxi Province in which industrial chemicals spilled into the Zhanghe River, Xinhua news agency quoted local officials as saying.

A loose drainage valve at an industrial plant in the city of Lucheng resulted in nine tons of the chemical Aniline spilling into the river. An additional 30 tons of the chemical were contained in a disused reservoir.

Aniline, which is used as a precursor in the manufacture of pigments, herbicides and polyurethane, can be toxic to humans.

The leak was first spotted by employees at the Tianji Coal Chemical Industry plant during a routine check on December 31, Xinhua quoted a company spokesperson as saying.

Screenshot from AP video

Scores of dead fish were reported in the river as early as Friday evening, though there have been no reports of human causalities.

While the city of Handan has cut off its water supply from the tainted reservoir located on the river, and switched to another underground water source, residents may have been exposed to the tainted water for around five days.

It is not known why the contamination alerts were delayed for such an extended period of time. News of the incident has led local residents to buy up bottled water from local supermarkets en masse.

"Since the pollutants won't decompose easily, it will likely take weeks to solve the problems caused by the spill," Zhang Xiaojian, a professor at the environmental school of Tsinghua University, told Xinhua.

Wide-scale economic growth in China has led to a number of large factories being built along rivers. Poor environmental controls at these factories and relatively lenient punishments for accidents has led to a rash of similar incidents in recent years.

In January 2011, the water supply for the city of Liuzhou was cut off after industrial waste spilled into the Longjiang River in south China's Guangxi Zhuang Autonomous Region.

And in 2010, the Songhua River in northeast China's Jilin Province was polluted after floodwaters swept warehouses owned by two chemical manufactures, spilling contaminants into the river.